docs: def convert2wavenumber(self):
          """
          Convert from wavelengths to wavenumber.
  
          Units:
            Wavelength: micro meters (1e-6 m)
            Wavenumber: cm-1
          """
          self.wavenumber = 1. / (1e-4 * self.wavelength[::-1])
          self.irradiance = (self.irradiance[::-1] *
                             self.wavelength[::-1] * self.wavelength[::-1] * 0.1)
          self.wavelength = None